In recent mobile communications, the distribution of rich contents such as Internet access, streaming broadcasting, music, and images is increasing and further a data communication application is expanding, instead of verbal communication-oriented communications in a conventional portable telephone.
In order to correspond to such a request, Mobile WiMAX is employing, for example, a TDD communication method.
Moreover, because a mobile terminal station (hereinafter, “terminal station”) for mobile communication has a wide dynamic-range received power received from a wireless base station, the terminal station performs a process for controlling the gain of a receiving amplifier to correspond to the change of the received power.
There has been known automatic gain control (AGC) as a mechanism that automatically performs a process for controlling a gain. The technique has been known as disclosed in, for example, Japanese National Publication of International Patent Application No. 2007-501547 and Japanese Laid-open Patent Publication No. 2003-124909. Specifically, in the case of AGO, a received power is measured and the adjustment of a gain is performed in accordance with the measured received power.
However, in the case of TDD communication, a wireless frame is time-divided into a downlink communication time that is used for communication from a wireless base station to a terminal station and an uplink communication time that is used for communication from a terminal station to a wireless base station. Moreover, when multi access by which a plurality of terminal stations communicate with one wireless base station is performed, the plurality of terminal stations performs communication within an uplink communication time (see FIGS. 13 and 14).
A terminal station adjusts the gain of the received power of an electric wave transmitted by a wireless base station in order to perform a reception. For example, because reception timing is not recognized by a receiver at initial synchronization such as the application of power, there may be a problem that the terminal station is difficult to correctly adjust a gain.
For example, when an own terminal station that performs initial synchronization is located at a long distance from a wireless base station and another terminal station that communicates with the wireless base station is located at the vicinity of the own terminal station, it is necessary to heighten a gain when amplifying a received signal because a received power emitted from the wireless base station becomes small. However, if a reception time and a transmission time are uncertain, the terminal station may receive a signal transmitted by the other terminal station to the wireless base station with large electric power when the terminal station is going to receive a signal from the wireless base station and thus a receiving system may cause a failure (see FIG. 15).
In the case of SOFDMA that is a multiple access scheme that is used for Mobile WiMAX, a subcarrier of OFDM is divided into some groups and a multiple access is realized by assigning the groups to the plurality of terminal stations.
In this case, a plurality of subcarrier groups transmitted from the plurality of terminal stations with maximum power is synthesized and is received by the own terminal station, and thus uplink communication is received with further large electric power.